Emerald is a Pokémon Trainer of unknown origins. Due to the loss of his parents at a young age, he was moved between his family members and was constantly bullied by his cousins due to his short height and tendency to rely on the help of Pokémon to get objects from high places. These events led to Emerald developing a complex about his height and a dislike of Pokémon. To get over his height issues, he used hair gel to style his hair upwards and wore various gadgets and clothing to make himself look taller than he actually is. He stops wearing these gadgets as well as his upwards hairstyle in the Omega Ruby & Alpha Sapphire chapter.

The constant moving from family member to family member led to Emerald developing the ability to determine a Pokémon's birthplace. If a Pokémon goes on a rampage, Emerald can calm it by surrounding the Pokémon with a "seal" of soil from its birthplace. The Pokémon is then calmed by a sense of nostalgia. For his skills, he is given the title of "Calmer" (鎮める者 Calmer).

Emerald claims to not like Pokémon themselves, but he likes Pokémon battles. To the amazement of the reporter, he is an expert at battling. As he does not train his own Pokémon, he borrows the Pokémon he uses from Crystal. Despite these claims, he is very close to Latios and Latias, who call him "Em".